The present invention relates to conductive connection between elements by using conductive paste. In particular, the present invention relates to an inter-electrode connection structure for effecting conductive connection between substrate side electrodes formed on a substrate and element side electrodes formed on electronic elements mounted on the substrate and to an inter-electrode connection method for realizing the structure. Further, the present invention relates to a semiconductor device formed so as to include an IC chip, and to a semiconductor mounting method for joining such a semiconductor device to an external substrate such as a PCB (printed circuit board). Further, the present invention relates to a liquid crystal device and an electronic apparatus produced by using the semiconductor device and the semiconductor mounting method.
Nowadays, a liquid crystal device is widely used as the visible image display section of various electronic apparatuses, such as a portable telephone and a video camera. Various kinds of semiconductor devices are arranged in such a liquid crystal device and electronic apparatus. By a semiconductor device it is meant here an IC chip, an IC structure in which an IC chip and a substrate are formed into an integral unit, or the like. Known IC chips include a bare chip IC which has undergone no packaging and an IC which has undergone packaging and which has terminals on its back side. Known examples of such an IC structure include a COB (chip on board), in which a plurality of ICs are mounted on a single substrate, an MCM (multi chip module), and a COF (chip on film) in which an IC is mounted on an FPC (flexible printed circuit).
Conventionally, when connecting a semiconductor device to an external substrate or, further, when joining a liquid crystal driving IC to a light transmitting substrate in a liquid crystal device, mounting methods such as wire bonding and TAB (tape automated bonding) have been used.
Further, when manufacturing the above IC structure, it is necessary to effect conductive connection of electronic elements such as IC chips to a circuit board such as a PCB. Conventionally, to effect such conductive connection, mounting techniques such as wire bonding technique and heat seal technique have been used.
However, in the case of the above conventional mounting methods for semiconductor devices, it is difficult to conduct minute pitch mounting. Thus, it has been difficult to correctly join a semiconductor device or the like having an electrode terminal of a minute pitch of 80 xcexcm or less, in particular, 50 xcexcm or less to an external substrate.
Further, in the case of the above-mentioned mounting technique related to the conductive connection between electrode terminals, it is impossible to connect electrode terminals to each other whose inter-electrode pitch is minute. Further, a large area is required for mounting. For example, in the connection method using the wire bonding technique, an inter-electrode-terminal pitch of approximately 130 xcexcm is the limit, and, in the heat seal technique, an inter-electrode-terminal pitch of approximately 240 xcexcm is the limit. Thus, it is difficult to connect electrode terminals arranged at a minute pitch of 80 xcexcm or less, in particular, 50 xcexcm or less.
In view of this, it is a principal object of the present invention to effect conductive connection of electrode terminals arranged at a minute pitch correctly and with high reliability.
In particular, the present invention has been made in view of the problems in the mounting technique related to the above mentioned conductive connection between electrodes. It is a first object of the present invention to provide an inter-electrode connection structure and an inter-electrode connection method in which conductive connection of electrodes arranged at a minute pitch can be correctly effected and in which the requisite area for the conductive connection can be reduced.
Further, the present invention has been made in view of the problems in the above mounting method for semiconductor devices or the like. It is a second object of the present invention to provide an apparatus and a connection method in which, in relation to the joining of a semiconductor element having minute pitch electrode terminals to a substrate, it is possible to achieve an improvement in the reliability of the joint portion and to achieve an improvement in yield.
To achieve the above objects, the inter-electrode connection structure, inter-electrode connection method, semiconductor device, semiconductor mounting method, liquid crystal device, and electronic apparatus according to the present invention are constructed as follows:
In the inter-electrode connection structure of the present invention, which is an inter-electrode connection structure for effecting conductive connection between a substrate side electrode formed on a substrate and an element side electrode formed on an electronic element mounted on the substrate, (1) the substrate side electrode and the element side electrode are arranged so as to be in contact with or close to each other, (2) a conductive paste is provided so as to connect the terminals at the contact or proximity portion, and (3) the conductive paste is applied to the contact or proximity portion of the terminals by being sprayed in particles.
In this inter-electrode connection structure, the conductive paste is placed on the terminals by spraying it in particles, so that, even when the electrode pitch is minute, it is possible to correctly place the conductive paste on each of the electrodes, whereby conductive connection between minute pitch electrodes is possible. Further, since the electrodes are connected to each other by using conductive paste, the conductive connection state is stable, thereby achieving an improvement in reliability. Further, since conductive connection is effected with a conductive paste in a particle form, the mounting area may be small.
In the above construction, the xe2x80x9cconductive pastexe2x80x9d is a paste-like or kneaded-matter-like soft conductive material, and is formed, for example, by dissolving an appropriate conductive material in solvent. Further, as the method for xe2x80x9cspraying the conductive paste in particlesxe2x80x9d, it is possible to adopt a well-known fluid spraying method, which has conventionally been known as an ink jet system or the like. This ink jet system can be realized by, for example, a well-known piezoelectric system, a well-known bubble spraying system or the like. The piezoelectric system is a method according to which a fluid such as ink is sprayed in particles by utilizing a force generated by supplying electricity to a piezoelectric element. The bubble spraying system is a method according to which a fluid is sprayed in particles while generating bubbles by partially heating the fluid by using a heat generating substance. It goes without saying that any other appropriate method can be adopted.
Regarding this inter-terminal connection structure, the following forms are possible.
(1) The light transmitting substrate of a liquid crystal panel can be used as the substrate, and a glass substrate with a built-in liquid crystal driving IC can be used as the electronic element. In this form, even when the glass substrate with a built-in IC is long, conductive connection of the glass substrate to the light transmitting substrate can be correctly effected. Further, since the area for the conductive connection may be small, it is possible for the liquid crystal panel to be made generally very small.
(2) A flexible or non-flexible printed circuit board can be used as the substrate, and a multi-layer IC chip can be used as the electronic element. Here, the xe2x80x9cmulti-layer ICxe2x80x9d is a semiconductor element in which a plurality of IC chips are stacked together. Generally speaking, in this multi-layer IC, wiring is provided on the side surface portion of the multi-layer structure, and the element-side electrode is provided at the forward end of the wiring.
(3) A flexible or non-flexible printed circuit board can be used as the substrate, and a plastic film liquid crystal panel (PFP) can be used as the electronic element. In the PFP, a pair of light transmitting substrates sandwitching the liquid crystal of a liquid crystal panel are formed not by a glass but by a plastic film. The PFP is lighter than a liquid crystal panel using a glass substrate, and, since it is a plastic film, it can be bent. In the present invention, conductive paste is supplied to the sections between the individual electrodes, so that, even in the case in which a plastic film that is easily bent is used as the substrate, conductive connection of each of the terminals can be correctly effected.
In the inter-electrode connection method of the present invention, which is an inter-electrode connection method for effecting conductive connection between a substrate side electrode formed on a substrate and an element side electrode formed on an electronic element, (1) the substrate side electrode and the element side electrode are arranged so as to be in contact with or close to each other, and (2) conductive paste is sprayed in particles to the contact portion or proximity portion of the electrodes to connect the electrodes to each other by the conductive paste.
The advantages of the inter-electrode connection structure and the inter-electrode connection method of this invention will be summarized: since the conductive paste is put on the section between the electrodes by spraying it in particles, it is possible to correctly put the conductive paste on each of the electrodes even when the electrodes are arranged at a minute pitch, thereby making it possible to effect conductive connection of electrodes arranged at a minute pitch. Further, since the electrodes are connected to each other by using a conductive paste, the conductive connection state is stable, whereby an improvement is achieved in terms of reliability. Further, since the conductive connection is effected by a conductive paste in a particle form, the mounting area may be small.
Further, in the inter-electrode connection structure of the present invention, the electrodes are connected individually by means of a conductive paste, so that conductive connection of the individual electrodes can be correctly effected even in the case in which the substrate with a built-in IC is long.
In accordance with the present invention, there is further provided a semiconductor device which has a built-in semiconductor and which is equipped with a plurality of externally exposed electrodes, wherein there is provided a conductive paste that is sprayed in particles and put on each terminal. The conductive paste put on the electrode can be used as a bump, that is, a protruding electrode. Examples of such a semiconductor device include a bare chip IC that is an IC before packaging, an IC which has undergone packaging and which has an electrode on the back side, COB, MCM and COF.
In this semiconductor device, a conductive paste is put on each electrode by spraying it in particles, so that the conductive paste in particle form can be correctly put on each electrode even in the case of electrodes arranged at a minute pitch, whereby it is possible to correctly effect conductive connection of electrodes arranged at a minute pitch without a hitch.
In this construction, it is possible to adopt the same xe2x80x9cconductive pastexe2x80x9d and method of xe2x80x9cspraying conductive paste in particlesxe2x80x9d as mentioned above.
Further, in accordance with the present invention, there is provided a semiconductor mounting method for joining a semiconductor device which has a built-in semiconductor and which is equipped with a plurality of externally exposed electrodes to an external substrate, wherein (1) a conductive paste is sprayed in particles at least to an electrode on the external substrate or to the terminal of the semiconductor device to put it on the electrodes and (2) relative positioning of the semiconductor device and the external substrate is effected to glue them to each other.
In this semiconductor mounting method, the conductive paste is sprayed in particles to thereby put it on the individual electrodes, so that it is possible to put the conductive paste in particle form correctly on the individual electrodes even when the electrodes are arranged at a minute pitch, whereby it is possible to correctly effect conductive connection of minute-pitch electrodes without a hitch. Further, since the electrodes are connected to each other by using a conductive paste, the conductive connection state is stable and an improvement in reliability is achieved.
Regarding this semiconductor mounting method, the following forms are possible:
(1) The semiconductor device conductively connected to the external substrate using the conductive paste may exhibit some fastening force itself. However, when a still firmer fastened state is desired, it is desirable that the semiconductor device be firmly attached to the external substrate by curing resin after gluing the semiconductor device and the substrate to each other. This curing resin may be supplied to the border region between the external substrate and the semiconductor device after performing relative positioning on them, or it may be supplied in advance to the section between them before performing relative positioning on them.
(2) The process of spraying the conductive paste in particles can be performed a plurality of times on the same part of the external substrate and/or the semiconductor device. This makes it possible to increase the height of the conductive paste put on the electrode in accordance with the times that the spraying is performed, whereby reliable conduction is obtained even when the recess of the electrode portion of the semiconductor device is deep.
(3) When the spraying of the conductive paste is executed a plurality of times as described above, it is desirable that a drying process be executed on the conductive paste sprayed on the external substrate and/or the semiconductor device before the next spraying of conductive paste is performed. This makes it possible to prevent the conductive paste from being crushed, whereby it is possible to effectively set the height of the conductive paste.
In accordance with the present invention, there is further provided a liquid crystal device which includes a pair of light transmitting substrates opposed to each other with a liquid crystal placed therebetween and a liquid crystal driving IC joined to at least one of the light transmitting substrates, wherein conductive connection between the electrode on the light transmitting substrate and the electrode terminal of the liquid crystal driving IC is effected through a conductive paste which is sprayed in particles and put on at least one of the electrodes.
In accordance with the present invention, there is further provided an electronic apparatus comprising a semiconductor device having a built-in semiconductor and equipped with a plurality of externally exposed terminals and an external substrate on which the semiconductor device is mounted, wherein conductive connection is effected between the electrode of the external substrate and the electrode terminal of the semiconductor device through a conductive paste which is sprayed in particles and put on at least one of the electrodes.
The advantages of the semiconductor device and the semiconductor device mounting method of the present invention will be summarized: since a conductive paste is sprayed in particles and put on the individual electrodes, it is possible to correctly put conductive paste in particle form on the individual electrodes even when the electrode terminals are arranged at a minute pitch, whereby it is possible to correctly effect conductive connection between minute-pitch electrodes without a hitch. Further, since the electrodes are connected to each other by using a conductive paste, the conductive connection state is stable and an improvement is achieved in terms of reliability.
Further, in a form of the semiconductor mounting method of the present invention, it is possible to fasten a semiconductor device to an external substrate in a simple and reliable manner.
Further, in another form of the semiconductor mounting method of the present invention, it is possible to increase the height of the conductive paste.
Further, in still another form of the semiconductor mounting method of the present invention, it is possible to effectively increase the height of the conductive paste.
Further, in the liquid crystal device of the present invention, it is possible to form the electrode terminals of a liquid crystal driving IC at a minute pitch, so that the size of the liquid crystal driving IC can be reduced when driving a liquid crystal panel of the same area.